Purse string sutures frequently are used in surgical procedures such as in cardiac surgeries wherein the heart, major arteries, and/or major veins are cannulated for cardiopulmonary bypass (CPB). More specifically, a purse string suture is used to seal the tissue around a cannula, a catheter, or the like, placed within the cardiac tissue.
Accordingly, a cardiopulmonary bypass procedure requires a cannula (or cannulae) to be placed into the right side of the heart (typically the right atrium) or in the major veins (typically the superior vena cava and/or inferior vena cava) to drain blood from the patient and deliver it to a pump-oxygenator, commonly known as the heart-lung machine, and then return the oxygenated blood to the body through a perfusion cannula. In some circumstances, the perfusion cannula may be placed into a large peripheral artery, such as the common femoral artery, however it generally is more acceptable to return the blood through a cannula placed directly into the ascending aorta.
The insertion of the arterial (aortic) perfusion cannula include the procedures of entering the patient's chest and placing two concentric purse string sutures into the anterior wall of the ascending aorta just proximal to upstream of the brachiocephalic trunk. The diameter of the purse string sutures are made large enough to accommodate the size of the aortic perfusion cannula, which are dictated by individual patient physiology. The cannula is inserted through a small incision made through the wall of the aorta into its lumen in the center of the purse string sutures. Typically the trailing ends of the respective suture threads then are each threaded through a "choker" tube or sleeve, sometimes referred to as a Romell tourniquet, which act as a tourniquet for tightening and securing the purse string sutures about the cannula. The purse string sutures are tightened by means of their respective choker tubes, and a suitable clamp such as a forceps is used to lock the trailing ends of the sutures within the choker tubes. The tightened and clamped purse string sutures seal the aortic wall around the perfusion cannula in order to prevent the escape of blood from, or the introduction of air into, the aorta. The venous drainage cannula(e) is similarly inserted directly through an incision centered within a single purse string suture into the right atrium of the heart or into the superior and/or inferior vena cavae, for connection to the drainage side of the pump-oxygenator. The cardiopulmonary bypass is instituted by allowing unoxygenated blood which is returning to the right side of the heart to be diverted into the pump-oxygenator where it is oxygenated and temperature-adjusted, and then pumped into the patient's arterial system via the aortic perfusion cannula.
In the construction of the purse string sutures, typically two concentric rows, with off-setting or staggered stitches and with each row having 4 to 5 stitches, are placed for the arterial perfusion cannula. Because the blood flow pressure is greater on the arterial side of the heart, a double purse string suture is used as a precaution in case one suture breaks. Two rows of stitches also help to minimize the risk of blood leakage from the incision site. On the other hand, because there are not the pressure concerns on the venous side, only a single purse string suture having about 5 to 6 stitches typically is used for venous cannulation. As the cardioplegia cannula is in a portion of the circulatory system that has been bypassed by CPB, there is virtually no concern of blood leakage, and only a single purse string suture is necessary to seal the tissue around the cannula and hold it in place. Examples of methods and apparatus for constructing purse string sutures are described in copending U.S. patent application Ser. No. 08/850,321, filed May 2, 1997, and entitled, Automatic Purse String Suture Device, which application is incorporated herein by reference.
Conventionally, purse string sutures are manually stitched by the surgeon or are applied by a surgical instrument such as those disclosed in the above mentioned patent application. In laparoscopic surgery, for example, where tubular ends of tissue are being tied off, the entire thickness of the tissue wall may be penetrated to achieve the desired suturing. However, in cardiac surgery, and particularly in the context of aortic cannulation, total penetration of the aortic wall by the purse string suture can cause catastrophic effects and thus, the surgeon must be cautious so as not to penetrate the entire thickness of the vessel wall.
As previously mentioned, up to the present time purse string sutures have been tightened and locked in place using tourniquets comprised of lengths of choker tubes to draw the trailing ends of the suture thread tight, and locking forceps to clamp the trailing ends within the tubes to lock the purse string suture. It follows that generally there are from three to five purse string sutures placed about two to four cannulae, thereby resulting in as many cannulae, choker tubes, and forceps within the surgical opening in which a surgeon is operating. The existence of these additional auxiliary instruments, though cumbersome, can be tolerated in a median sternotomy construction where the chest is fully opened and a relatively large surgical opening is provided. However, this is not the case in a minimally invasive construction such as a mini-thoracotomy or mini-sternotomy where the space within a surgical opening is very restricted. Thus, the use of the high profile choker tubes and forceps to secure the purse string sutures in place about the cannulae is highly disadvantageous since such auxiliary instruments obstruct the surgeon's ready access to the surgical site. With the progression towards less invasive cardiac surgical techniques which require the visualization and manipulation of surgical instruments through less invasive openings in the chest, there is a need for compact surgical instruments, particularly auxiliary instruments, to improve upon the space which is available to a surgeon for viewing the surgical site as well as for accommodating the surgeon's hands.
Another objective of less invasive surgeries is to reduce the time a patient is subjected to potentially traumatic procedures, such as the necessary clamping of the aorta prior to implementing CPB and thereby reduce the interruption in systemic circulation. Likewise, it is desirable to reduce the amount of time it takes to perform the more menial tasks during, for example, placing a cannula, such as tightening and securing the purse string sutures, and for subsequently removing the purse string sutures after the completion of surgery.
Accordingly, it would be highly desirable to provide a choking or clamping device for tightening and securing a purse string suture about a cannula and the like, wherein the clamping device is small and unobtrusive, is readily applied and removed and thus is optimally adapted to minimally invasive surgical procedures. In addition, it would be desirable for the clamping device to continuously provide a constant, predetermined tension to a purse string suture.